Compositional Effect on the Low-Temperature Oxidation of Crude Oils Subjected to In Situ Combustion

This work shows the compositional effect on low-temperature oxidation of crude oils subjected to in situ combustion (ISC). Three heavy crudes were used in this study in which detailed information on the molecular species involved in ISC was obtained by ultra-high-resolution mass spectrometry. The oxidation was carried out on a mixture of 2% of crude oil in Ottawa sand in an isothermal cell using a batch system at 1500 psi at three conditions: (i) reservoir temperature of each crude oil, (ii) 180 °C, and (iii) 180 °C using a heterogeneous catalyst-type β-MnO2. The oil remaining after the reaction was extracted from the sand and characterized by FT-ICR MS using (+) atmospheric pressure photoionization and (−) electrospray ionization modes. The acidity of the oxidation products (extracts) and the composition of the produced carbon oxides were also monitored. A greater amount of carbon oxides produced, a lower extraction yield of organic matter in the sand after the reaction, and a higher acidity in the extracts, implied a higher reactivity. In the same sense, a higher reactivity was observed for the sample with the highest sulfur content and over the most aromatic compounds. The use of the catalyst at 180 °C promoted the oxidative reactions in two of three of the oils, as well as the formation of polyoxygenated acids over monocarboxylic acids for one of the oils, which implies that the application of this technology strongly depends on the composition of the oil.